Kutorginata (Order: Kutorginida)
Nisusia belongs within the Family Nisusiidae.
Nisusia – from the Latin, nisus, meaning “labored, or striven.”
burgessensis – from Mount Burgess (2,599 m), a mountain peak in Yoho National Park. Mount Burgess was named in 1886 by Otto Klotz, the Dominion topographical surveyor, after Alexander Burgess, a former Deputy Minister of the Department of the Interior.
Syntypes –USNM69690-69697 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Burgess Shale and vicinity: Nisusia alberta from the Trilobite Beds on Mount Stephen (Walcott, 1905, 1908). The Burgess Shale brachiopods, in particular from the Trilobite Beds on Mount Stephen, need to be re-examined (see also Brief history of research).
Other deposits: Several species are known in the Lower-Middle Cambrian of North America, Greenland, Russia, China and Australia.
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
The Walcott Quarry on Fossil Ridge.
Brief history of research:
Nisusia burgessensis was originally described as Orthisina alberta (Walcott, 1889) before being renamed Nisusia alberta (Walcott, 1905). Specimens of this species identified from the Walcott Quarry (Walcott, 1912) were re-described by Walcott as Nisusia burgessensis (Walcott, 1924), a combination still in use today. This species has not been studied since and is in need of revision.
This species has fine radiating ornamental lines (costae) and concentric lines of growth. The shell was originally mineralized. It is roughly 1.5 wider than its length. Both valves are convex, but the convexity of the ventral shell is more pronounced. The shells would have been articulated with short and small teeth, like in Diraphora, a comparable form from the Burgess Shale. Very thin bristles (setae) are present in a single specimen at the front of the shell margin. These would have been attached to the edge of the mantle along both the dorsal and ventral valves in the same way as in Micromitra.
Nisusia burgessensis is relatively common in the Walcott Quarry but overall represents a small fraction of the fauna (<0.3%) (Caron and Jackson, 2008).
Nisusia probably had a relatively short, stout pedicle attached either to the substrate or to other organisms like the sponge Pirania, to raise it above the sediment-water interface. In this way the brachiopod would have been relatively protected from flocculent mud travelling along the sediment-water interface, which could have been detrimental to its filter-feeding apparatus (located between the shells) called a lophophore. The bristles (setae) might have also helped reduce the intake of mud particles into the filter-feeding apparatus.